Episode 194: STS-100 - Giving the ISS a Hand (ISS 6A: Canadarm2)

The ISS is growing so much that soon the shuttle arm won’t be able to help attach new modules. So let’s give the ISS an arm of its own! We’ll also wonder just what happened to the Command and Control computers, and try to blink our way through our problems.

Episode Audio #

Photos #

For more photos, head over to our friends at Wikiarchives.space: https://wikiarchives.space/index.php?/category/877

Videos #

Space Shuttle Endeavour lifts off on STS-100.

An animation depicting Endeavour’s approach path to the front of the ISS.

Moving the pallet containing Canadarm2 to its temporary position on the Destiny lab.

Moving the other end of Canadarm2 to the permanent Power and Data Grapple Fixture.

Installing the MPLM.

The station arm handing off the space pallet to the shuttle arm for return to Earth.

An overview of EVA 1.

An overview of EVA 2.

Endeavour landing at Edwards.

Crew Activity Report 1. If this looks rough, just be glad I converted it from Realplayer first!

Crew Activity Report 2.

Crew Activity Report 3.

Crew Activity Report 4.

Crew Activity Report 5.

Crew Activity Report 6.

Crew Activity Report 7.

Post-Flight Presentation #

To see the mission in motion, check out the post-flight presentation! Click here for full video details.

Transcript #

NOTE: This transcript was made by me just copying and pasting the script that I read to make the podcast. I often tweak the phrasing on the fly and then forget to update the script, so this is not guaranteed to align perfectly with the episode audio, but it should be pretty close. Also, since these are really only intended to be read by myself, I might use some funky punctuation to help remind myself how I want a sentence to flow, so don’t look to these as a grammar reference. If you notice any egregious transcription errors or notes to myself that I neglected to remove, feel free to let me know and I’ll fix it.

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Hello, and welcome to The Space Above Us. Episode 194, Space Shuttle flight 104, ISS 6A, STS-100: Giving the ISS a hand

Before we get into things today, I’ve got a brief personal update. First, since people frequently ask, grad school is going well, thank you. I just wrapped up Non-Linear Systems, Dynamics, and Control and somehow pulled off an A. I’ve got the summer off and then starting in late August I dive into Space Traffic Management, which has a reputation for requiring a lot of work. So despite best intentions, you can probably count on another regrettable gap in the schedule. We’ll see. I’ll do my best.

Second, I thought it was worth mentioning that I have once again had a space mission canceled out from underneath me at work. Long time listeners will recall that I worked on Restore-L, which became OSAM-1, and which was subsequently was canceled in late 2024. After that, I helped build a tool that would facilitate answering attitude questions during the transit phase of the Lunar Gateway, a small space station that was planned to hang out near the moon in a fancy orbit called a Near-Rectilinear Halo Orbit. Basically the tool answered “in the year it takes to get to the moon in this slow spiral, where should we point the station?” When the attitude tool was finished, I was actually invited to join the Gateway Mission Design team which.. awesome! But as those who are listening in realtime will still remember, Gateway was canceled in early 2026. Not so awesome.

I’m bringing this all up not to be a downer. Actually kind of the opposite. This experience has been yet another reminder that you never know where life is going to take you. Because what happened to the folks who were working on Gateway Mission Design? We got pulled onto Artemis Mission Design, helping to craft the trajectories that will be used by the upcoming crewed lunar missions. You guys.. I’m gonna send people to the moon.

I’m not really going to be able to talk about it here since it’ll be too tricky for me to keep track of what is public information and what isn’t, and since I’d probably have to get everything cleared with the Public Affairs Office, but I thought listeners here would appreciate knowing what I’m up to. But with that said, if anyone really wants to get into the weeds, shoot me an email at jp@thespaceabove.us and I can direct you to some publicly available conference papers written by people on my new team which explains the process of creating these trajectories in an era when computers are just a little more powerful than they were in the 60s.

I won’t belabor this, because we have a lot to get into today, but I did want to say that a few weeks ago as part of this new role at work I finally had the opportunity to visit the Johnson Space Center for the first time, and among other things I got to see the Shuttle Avionics Integration Laboratory, or SAIL, which I’ve apparently only mentioned once in passing, on the STS-79 episode. The SAIL is a testing facility that has all same electronics, wiring, computers, and so on as a real space shuttle, but out in the open and easier to access. It’s where they tested new equipment and procedures with maximum realism. I bring this up because remember how on the last episode there was that incident a general purpose computer was turned on slightly too fast? Well, while I was sitting in the commander’s seat of the SAIL I impressed (and sort of confused) the person showing me around when I remembered what panel the GPC controls were on and reached up to see for myself what the startup procedure was like. And now I can absolutely see how it would be easy to accidentally flip the switch a little too fast. This podcast has filled my brain with so much weird information. Anyway, let’s get started.

Last time, we flew along on Space Shuttle Discovery for STS-102, swapping out the crew of the International Space Station and debuting the Multi-Purpose Logistics Module. We also learned the hazards of booting up space shuttle computers too quickly, as well as the hazards of having procedures that don’t include a rationale for why they’re important. STS-102 departed and the second crew of the ISS began settling in to their new home, the baton successfully passed.

Today, we’ll take a step back in the mission numbering scheme to STS-100, also known as ISS assembly flight 6. The goal today will be to transfer another load of supplies and experiments in a second Multi-Purpose Logistics Module, as well as delivering and installing one of the most sophisticated robotic systems ever used in spaceflight: Canadarm2.

Our crew today has people from more countries than any previous spaceflight, with four of the five major ISS partners being represented.

Commanding the mission is Kent Rominger. We know Rominger from a bunch of flights, but most recently as the commander of STS-96, a logistics and resupply mission to the ISS a couple of years ago. This is Commander Rominger’s fifth and final flight.

Joining Rominger up front is today’s pilot, Jeff Ashby. When we last saw Ashby he was riding shotgun with Eileen Collins, dodging golden bullets and delivering the Chandra x-ray telescope to orbit. This is his second of three flights.

Behind Ashby we have a fan favorite returning for the first time in a while: Mission Specialist 1, Chris Hadfield. We last saw this Canadian astronaut on STS-74 which delivered the docking module to Mir around six years previously. Hadfield will be one of two spacewalkers installing his country’s latest robotic creation to the exterior of the ISS. This is his second of three flights.

Sitting in the middle of the flight deck is Mission Specialist 2, John Phillips. John Phillips was born on April 15th, 1951 in Fort Belvoir, Virginia. He earned a bachelor’s in mathematics from the US Naval Academy, and later picked up a master’s in aeronautical systems from the University of West Florida, and another master’s and a PhD in Geophysics and Space Physics from UCLA. In between all that he served as a naval aviator, flying the A-7 Corsair and CT-39 Sabreliner, racking up 4500 flight hours and 250 carrier landings. He also worked for nine years at the Los Alamos National Laboratory, doing research on the sun and space environment. As if all that wasn’t enough, he was the principal investigator of the Solar Wind Plasma Experiment on Ulysses, the spacecraft we deployed on STS-40 back in 1990. Phillips was selected as an astronaut in 1996 and this is his first of three flights.

Down on the middeck we have another familiar face: Mission Specialist 3 Scott Parazynski. We last saw Parazynski on STS-95, doing a bunch of important science research on SPACEHAB, deploying and retrieving the free-flying SPARTAN payload, oh, and flying with some guy you may have heard of named John Glenn. This is Parazynski’s fourth of five flights.

Next to Parazynski is Mission Specialist 4, Umberto Guidoni. When we last saw Guidoni it was under less than ideal circumstances on STS-75 as the reflight of the Tethered Satellite System somehow ended up even worse than the first flight. At least they got some data the second time. Guidoni is double lucky on this flight since for reentry he’ll be swapping with Hadfield on the flight deck, instead of the usual MS3, perhaps because Parazynski has had plenty of opportunities to see the plasma light show. He’ll also become the first European astronaut to float foot on the ISS. This is his second and final flight.

Last but certainly not least, we have Mission Specialist 5, Yuri Lonchakov. Yuri Valentinovich Lonchakov was born on March 4th, 1965 in Balkhash in the Dzhezkazgan Region of what is now Kazakhstan. He graduated with honors from the Oresburg Air Force Higher Military Pilot School as a pilot engineer and later graduated, again with honors, from the Zhukovski Air Force Academy as a pilot-engineer researcher, specializing in flight vehicles and testing their systems. He also served as a brigade commander in the Russian Air Force, logging more than 1500 hours on various aircraft, including the Yak-52, L-29, L-39, Su-24, A-50, Tu-16, and Tu-134. And I guess he sometimes got sick of flying in airplanes because he also jumped out of them 530 times. He was selected to become a cosmonaut in 1997 and this is his first of three flights.

Space Shuttle Endeavour clearly was eager to get going because the countdown proceeded smoothly with no delays. On April 19th, 2001, at 2:40 and 42 seconds PM Eastern Time, the vehicle lifted off the pad and STS-100 was underway. The phasing, rendezvous, and approach all proceeded without incident and the orbiter docked at the front of the Destiny laboratory around 43 hours into the mission. In a maneuver that is now familiar to us, the crew performed what Mission Specialist Scott Parazynski called the “PMA Shuffle”. Since Hadfield and Parazynski had an EVA coming up, the shuttle was at a lower atmospheric pressure than the ISS, so the hatches in both spacecraft couldn’t be open at the same time. But that didn’t stop the ISS crew from opening their end and dropping off some tools for the EVA before closing the hatch, allowing the shuttle crew to open their hatch, retrieve the tools, and drop off some water containers, mail from home, fresh fruit, and some other critical supplies.

Alright, so we got a little rendezvous and docking practice in and got the ISS crew some fruit that hasn’t been freeze dried, time to head home, right? Well, not quite yet. First we have to introduce one of the most sophisticated bit of robotics to ever fly in space: the Space Station Remote Manipulator System, or SSRMS, or more commonly: Canadarm2. Of course, we’re well familiar with Canadarm2’s little cousin, the Shuttle Remote Manipulator System, or Canadarm. If there’s one thing I’ve learned from this podcast it’s to never underestimate the value of a payload bay and a robot arm. For dozens of missions, the Canadarm has proven itself to be an invaluable asset on any shuttle flight, deploying and retrieving payloads, serving as a mobile work platform for spacewalks, and on STS-41D: a pee icicle remover.

But Canadarm2 was more than just a copy of the shuttle arm for the ISS. It was bigger, stronger, and more capable in just about every way. Let’s just go through some of the stats. The new station arm was 2.6 meters longer and 2 centimeters wider than the shuttle arm, with each of the two parts of the arm comparable to a telephone pole. The shuttle arm could move an impressive 29,937 kilograms of mass, but the station arm could move nearly four times that: an incredible 116,000 kilograms. Considering that on this particular flight Endeavour’s mass at liftoff, including payloads, was 103,504 kilograms, that meant that Canadarm2 could easily move the spacecraft that had delivered it to orbit. Part of the tradeoff was that the new arm was heavier and slower, but with so much added capability it was well worth it. Plus, Canadarm2 had an extra trick up its sleeve, or rather, up its shoulder. The shuttle arm had six degrees of freedom: two in the shoulder, one in the elbow, and three in the wrist. Canadarm2 had seven degrees of freedom, including an extra one in the shoulder. Why? Because unlike the shuttle arm, which was firmly attached to the orbiter at the shoulder, the station arm had an end-effector on both ends. This meant that it could move from grapple point to grapple point, end over end, sort of like an inchworm. According to Chris Hadfield, the word for such a motion is “pedipulate” and I’m just gonna take his word on that one. Now the extra degree of freedom in the shoulder makes sense; it’s not really a shoulder, it’s just another wrist.

The result was a robot arm that was even more capable than the shuttle arm, but which could be moved around the station to wherever it was needed, well beyond the range that the shuttle arm could reach while docked. This will be an essential capability on the very next flight when we deliver the station’s new airlock. In return for this contribution, Canada earned 2.3% of the space in the non-Russian segment of the station, and the right to send one astronaut up for a long duration stint every three years. Not a bad deal!

As I mentioned, the hatches between Endeavour and the ISS remained closed at first in order to facilitate the first EVA, which took place on flight day 4. Just before the EVA crew got started, pilot Jeff Ashby used the arm– jeez, I’m gonna have to specify which arm now– used the shuttle arm to move a pallet of equipment from Endeavour’s payload bay to that trunion pin up on the top of the Laboratory module. The pallet included Canadarm2, securely bolted down for the ride to orbit, as well as a new antenna that we’ll talk about in just a moment.

We’ve talked about a lot of spacewalks over the years, and I think even with something as incredible as a human venturing out into space in nothing but a spacesuit there is a tendency to get used to it and forget how magical it really is. Well, lucky for us, in addition to being a pilot and astronaut, Chris Hadfield is an accomplished author. And in his first book, “An Astronaut’s Guide to Life On Earth”, he wrote vividly about the experience. I’d like to read a couple of quotes I pulled from the chapter about this mission. This is a few different snippets but I’m just going go ahead and read it all together like it’s one thing. Hadfield wrote:

”Intellectually, I’d known I was venturing out into space yet still the sight of it shocked me, profoundly. You’re in a self-contained bubble, cut off, then you look up from your task and the universe rudely slaps you in the face. It’s overpowering, visually, and no other senses warn you that you’re about to be attacked by raw beauty. Another analogy: Imagine you’re in your living room, intently reading a book, and then you look up casually and you’re face to face with a tiger. No warning, no sound or smell, just suddenly that feral presence. It’s vast and overwhelming, this visual immersion, and I could drink it in forever - only here’s Scott, out of the airlock, floating over toward me. We get to work."

Pretty incredible words from the man who was the first from his nation to venture outside a spacecraft. But he’s right, we need to get to work. First, while I believe this was actually installed later in the spacewalk, let’s get that antenna out of the way. This is a UHF antenna that kind of looks like a six foot long double-ended q-tip, and was installed on the exterior of the Destiny laboratory. The antenna allowed better space-to-space communications, allowing the station to speak directly with both spacewalkers and the shuttle. It’ll be super useful during rendezvous and prox ops as well as during spacewalks. It will even allow the shuttle to issue commands like setting the ISS control mode to free-drift right before undocking. Before this, if the station crew wanted to get a message to the shuttle crew or spacewalkers they’d either have to tell the ground and have the ground tell them, or use a temporary VHF radio which was not very capable, and I believe couldn’t talk to the spacewalkers at all. With so many spacewalks to come, this was an essential capability.

The main task of this EVA was to essentially unpack Canadarm2. Launching into space is a pretty violent process, with a lot of intense forces and shaking. And robot arms are pretty sophisticated pieces of equipment that aren’t wild about being violently shaken. So with that in mind, the arm was locked in place by eight huge “superbolts” which were four feet long, about 1.2 meters, and 32 smaller bolts that helped hold the superbolts in place. With Hadfield on the end of the shuttle arm and Parazynski free-floating, the duo got to work carefully removing the bolts, storing the superbolts in a container that was dubbed the “quiver”. The moment the first bolt came off was actually a pretty big deal. As Mission Specialist John Phillips pointed out, once the first bolt came out they were committed. The crew simply did not have the equipment and facilities required to re-torque the bolts and re-secure the arm. The SSRMS was now here to stay.

Once the bolts were out, the duo loosened some special expanding fasteners, allowing the entire arm to move freely along its joints. Then they manually pushed the long arm segments, unfolding the apparatus, before getting to work re-tightening those same expanding fasteners to rigidize the structure. This was around five hours into the EVA and it was right around this time that Chris Hadfield noticed that his drinking water bag seemed to be leaking, with little drops floating around in his helmet. Not a great situation, but not the end of the world. But right after that he experienced significant pain in his left eye, which he later described as feeling like a large piece of grit had been smashed into his eye. Of course, being human, he reached up to rub his eye only to bounce off the visor of the spacesuit. Oops.

So far this is annoying but not really a big deal. Hadfield can’t see out of his left eye, but he can still see out of his right and there doesn’t seem to be any sort of emergency, so he keeps working and doesn’t bother telling the ground. There’s no immediate danger since he’s still tethered, and is even on the end of the shuttle arm, which can move him around. He keeps blinking and shaking his head, trying to clear the irritation without luck, but also keeps working on the expandable fasteners. But then the situation evolves. Hadfield is in weightlessness, so the tears his left eye is putting out don’t run down his face, they just sort of hang there in a big, and growing, blob of fluid. Eventually the blob gets big enough that it crosses the bridge of his nose and gets into his right eye. Now we have a problem. Both his eyes are burning and his vision is a blurry mess. This is.. very bad!

With no other option, Hadfield finally loops the ground in on the situation. Folks on the ground are immediately concerned the eye irritation could be caused by a leak in the CO2 scrubbing system, which uses lithium hydroxide, which is toxic. They ask him to open the purge valve in his helmet to vent out the air, just in case it’s contaminated. As Hadfield wrote in his book, “So now I’m blind, listening to a hissing noise as my oxygen merrily burbles out into the universe.”

After around 20 minutes of blinking as hard as he could and continuing to shake his head, Hadfield’s vision began to return enough that while it’s still a mess he could continue to work. So he and Parazynski wrap up this first round of work with the arm and head back inside, wrapping up a spacewalk that had some tense moments but was ultimately successful, adding 7 hours, 9 minutes, and 51 seconds to the log.

So what happened? It took the ground some time to think of the likely cause. Clearly it wasn’t the lithium hydroxide since Hadfield wasn’t coughing and like, dying. The clue comes from the leaking water bag. On their own, a few droplets of water floating around is annoying but not a big deal. But in this case, what seems to have happened is the water bounced into the interior of the helmet visor, which had been coated with an anti-fogging agent. Then that ball of water and anti-fogging agent drifted into Hadfield’s eye, and the anti-fogging agent caused severe irritation. In the end, this was nothing but an annoyance, but it was yet another reminder that in space the smallest thing will get you. And while it’s so far in the future that it’s beyond the scope of this podcast, this isn’t the last time that a water leak in an EMU helmet causes a problem. Just ask Luca Parmitano.

With the first EVA out of the way, the STS-100 crew were free to bring their cabin pressure up to match the station’s, and the next day it was time for the two crews to open the hatch and meet up. As the shuttle crew floated into the US lab module, Mission Specialist Umberto Guidoni became the first European to enter the ISS, claiming his own little slice of spaceflight history.

Space missions are always hectic, with such limited time and so much to do, and all the more so at a time like this with ten people all crowded into the same space. So with this in mind, Commander Kent Rominger had talked to the US and Russian mission control folks ahead of time and ha carved out an hour and a half block on the schedule so that the combined crews could enjoy a meal together. And wanting to do something special, Rominger made the meal luau themed, and everyone on both crews got some colorful Hawaiian shirts to mark the occasion. If you’d like to see photos of the color explosion that is the crew group photo, be sure to check the show notes page.

Around five hours later, the next significant event got underway, with the shuttle arm grappling a now-familiar structure in the payload bay: a Multi-Purpose Logistics Module, or MPLM. Leonardo, which we met last episode, landed back on Earth less than a month ago, so this is another MPLM named Raffaello. Same thing though: a big tin can that made it easier to move a bunch of cargo to and from the space station. Once the crew had the MPLM on the end of the shuttle robot arm they were able to bring it over to the underside of the Unity node and berth it. Once the Common Berthing Mechanism bolts did their thing and it was sealed in place, the crew were able to open the node hatch and start transferring equipment in through the wider CBM opening. Among other things, the MPLM contained two more EXPRESS racks, the standardized racks that essentially made up the walls of the Destiny laboratory. EXPRESS rack 1 had to be moved somewhat quickly since it was actually powered, even in the MPLM, and could not be unpowered for longer than 30 minutes without risking the plant growth and biological crystal growth experiments mounted inside it. So after being floated up out of the MPLM it was a quick 90 degrees forward, and into the US laboratory module for installation. Rack 2 was a more leisurely move since it wouldn’t even be activated until after the shuttle crew left, but it was noteworthy for carrying the Active Rack Isolation System, which as the name implies would help isolate sensitive experiments from vibrations and disturbances from the station crew moving around.

Among the cargo on this flight were nine science experiments, including the first three American commercial payloads. We won’t get into all the experiments since this episode is already going to be pretty long and, after all, we’ve already checked the box on the mandatory crystal experiment for this episode.

One fun thing about the MPLM is that when it came time to store empty bags and other trash, the crew set up a big net of bungee cords to hold stuff in place. But it quickly found a second use as a sort of weightless trampoline. The crew would come crashing into the bungees and get shot back out into the node.

The next day it was time for the flight’s second EVA and it was another complicated one. On EVA1, Hadfield and Parazynski had completed the initial deployment of Canadarm2, but they had left it still attached to the temporary pallet that was used to transport it to space. This was no big deal though, thanks to a neat capability of the new arm. Remember when I introduced the arm I mentioned that it had the capability to sort of walk, end over end? Well in between the spacewalks, the crew had the arm’s free end move over and grapple a permanent fixture on the exterior of the lab. Of course, we’re familiar with the shuttle arm grapple fixtures from dozens of various payloads. It basically looks like a circle with a nail sticking straight out of it. The end effector of the arm moves over the nail-like appendage and slides cables around it to hold the object securely on the end of the arm. That worked great for the shuttle arm because one end of that arm was always attached to the shuttle, which provided electricity. But how do you do the same trick with an arm that can move from grapple point to grapple point?

The answer is the “Power and Data Grapple Fixture”, or PDGF, that I mentioned a couple episodes back. As the name implies, this is a grapple fixture that looks similar to the standard grapple fixture we know and love, but which also conveys electrical power as well as data connections. By moving from fixture to fixture, Canadarm2 would always have a source of power and a data connection that would allow the crew to connect it. And it just so happens that on STS-98, a PDGF was installed on the exterior of the US laboratory! How convenient, it’s almost like they planned this!

The only trick is, the power and data connections that are supposed to be part of that fixture are currently connected to the temporary fixture on the pallet. So with one end of Canadarm2 on the temporary grapple fixture and one on the unpowered fixture, the goal of today’s EVA would be to disconnect the power and data lines from the temporary fixture and connect it to the permanent fixture. Got all that? Let’s head outside.

Chris Hadfield wrote in his book that after the incident during the first EVA he was determined to not let some stray visor coating cause another problem. So while preparing to head outside he wiped his visor so vigorously that he was surprised that he didn’t just rub right through the thing. Once outside, Parazynski hopped onto the Portable Foot Restraint on the end of the shuttle arm and headed over to start the grapple fixture reconfiguration, while Hadfield began climbing up to the starboard side of the Unity node. Let’s stick with Hadfield for the moment.

When I read what Hadfield’s task was I had to double check some notes because I could’ve sworn we did this already: removing the early communications antenna from the side of Node 1 to make room for a new module coming up on the next mission. Turns out I was right, we did already talk about that, but it was the port side, to make room for PMA-3. Now Hadfield would be removing the starboard antenna to make room for the upcoming airlock. This was pretty straightforward, except the wing nut connector just sort of fell apart, causing the wing nut and three screws to be lost underneath the CBM thermal cover. Hadfield went hunting around inside trying to find the debris but was ultimately unsuccessful. This wasn’t great since it could potentially impact the berthing of the airlock module on the next mission but there wasn’t anything to be done, so he headed back to the laboratory to help Parazynski.

Meanwhile, Scott Parazynski has been opening up panels on the exterior of the laboratory and doing some pretty complicated rewiring. This would have been tricky enough already, given the limitations of the spacesuit gloves, but it was made worse by the fact that other cables from previous missions were now on top of the work area, so the cables Parazynski needed were at the bottom and had to be carefully brought up and over. Even worse, some of these cables were actually delicate fiber optic lines, which can easily be snapped. This initially went fairly smoothly, but then the backup power supply failed to work, so Hadfield and Parazynski had to spend two hours carefully disconnecting, inspecting, and retorqueing connections from STS-98. In the end, they were successfully able to get the PDGF powered up and headed back inside after 7 hours, 39 minutes, and 22 seconds.

On flight day seven, one of the main activities was going to be using the new station arm to help move the pallet it was delivered on back to the shuttle payload bay, but the crew were faced with an unexpected snag. The International Space Station is controlled by three Command and Control computers, which handle the critical task of relaying commands from mission control to other systems about the station. Only one was really necessary, but three were included for redundancy since that way if one fails you just move over to another one and you still have yet another backup waiting in the wings. And even if that one fails, you switch to your final backup while you figure out what’s going on. I mean, what are the odds that all three computers fail at basically the same time? Well folks, you’re not gonna believe this, but that’s exactly what happened. Well, maybe.

I do have to caveat this by saying despite many hours of my best efforts I’m still not exactly sure of the precise sequence of events here, or even exactly what took place. Every source has a slightly different take on what happened when and why. The most detailed explanation, and the one that makes the most sense to me, comes from the book “Creating the International Space Station” by David Harland and John Catchpole, so I’ll mostly be relying on them for this section, but even then things don’t fully line up, so I guess we’ll just have to take this with a small grain of salt.

Late in the crew’s day on flight day six, the primary computer, C&C-1, failed, leaving mission control to work the problem overnight as the crew slept. One step the ground took was to reconfigure it into “standby” mode instead of the usual “primary” mode, and I believe they also used this opportunity to switch command and control to the backup computer C&C-2, but this is one of several key details I wasn’t able to definitively nail down. When the crew woke up on flight day seven Houston demonstrated they were able to use C&C-1 to turn a light on and off in the US lab module, which was good, but when Expedition 2 crew member Susan Helms attempted to transfer a data file from C&C-1 to the Robotic Workstation in order to work with the new robot arm, the computer failed. So the problem wasn’t quite solved yet. Not wanting to miss out on the fun, C&C-3 failed too. So now we’ve just got a single computer running things on the ISS. Not great.

Over the next few days, people on the station and on the ground worked through various troubleshooting steps with the computer, downloading diagnostic data, uploading new software patches, rebooting them, and so on. They also removed a backup payload computer from the Destiny module and loaded the C&C software onto it so it could replace C&C-1.

What’s confusing about this story is that most sources are light on details but agree that all three computers failed and that this left the ISS with no way to communicate with the ground, requiring everyone to route communications through Endeavour. This would be a big deal because it meant that the common berthing mechanism holding the MPLM to the node couldn’t be controlled, so the MPLM was stuck in place. It also meant that if Endeavour had to leave in a hurry there would be no way to command the ISS to release the orbiter and they would have to do an emergency undocking, leaving parts of the docking system behind. But none of that is mentioned in Harland’s book, which is the only source that took the time to go through most of the beat by beat events.

So how about we go with this: some of the command and control computers failed, which as the name implies meant there was limited ability to command and control the ISS from the ground. Some of the computers were fixed, and a backup computer was promoted to primary C&C computer, replacing one that was taken home for a more thorough diagnostic. Done.

Whatever exactly happened, it delayed the shuttle’s departure for a day while the issue could be worked, which had the knock-on effect of delaying the upcoming Soyuz-TMA 32 launch since if it arrived while Endeavour was still there it would pass uncomfortably close to the orbiter’s tail.

The extra day wasn’t a waste though, with most of the crew taking the time to continue packing the MPLM full of stuff to bring home. And presumably playing around with their weightless trampoline some more.

Once the computer problem was resolved the station crew was finally able to use their fancy new robot arm. Its first order of business was to pick up the pallet that had delivered it to the ISS in the first place up off of the Destiny module and hold it out for the shuttle arm to grab onto, in a sort of passing of the space hardware baton. Once the shuttle arm had a firm grasp on the pallet, the station arm could let go, and the crew could use the shuttle arm to place the pallet back in the payload bay for return to Earth.

On flight day eleven the crews said their goodbyes, the hatches were closed, and Space Shuttle Endeavour began to back away a little over eight days after arriving. Already, the addition of the new Space-to-Space Orbiter Radio was proving useful, facilitating communications during the undocking and flyaround. With pilot Jeff Ashby at the controls, Endeavour passed around the orbiting complex as the shuttle crew took reference photos of the station exterior. And in fact, they did a little more than take reference photos. Ashby was careful to keep Endeavour pointed at a specific angle relative to the station, ensuring that an IMAX camera in the payload bay would get some great footage as the orbiter flew around the station.

The crew was leaving the ISS with a critical new capability with the new robot arm, as well as dropping off nearly 2,900 kilograms of cargo, including 600 kilograms of water and over a ton of EXPRESS racks, and bringing 700 kilograms of waste and old equipment home. It also left a station with all three command and control computers operational, even if one was secretly a backup for the lab module.

Once clear of the station, Endeavour’s crew still had a little time to enjoy the view out the window before coming home. After the first and second landing opportunities at the Kennedy Space Center had to be waved off due to bad weather, and with a poor weather forecast for the foreseeable future, Rominger and Ashby guided Endeavour to a safe touchdown at Edwards Air Force Base, 11 days, 21 hours, 30 minutes, and 1 second after lifting off from Florida.

I think it might be easy to overlook this mission since Canadarm2 is, compared to the modules, pretty small physically speaking. But its capabilities cannot be overstated. The ability for both the crew and operators on the ground to move cargo, install new modules, and someday to snag commercial cargo vehicles right out of their orbits, is a huge asset. Plus, the flight also proved that Chris Hadfield was a pretty cool customer in a crisis. Something tells me he’ll have “ISS Commander” on his future resume.

Next time.. I think we’ve all learned a lot about the space shuttle and how it works over the last hundred or so episodes. But what if your life was on the line, as well as the lives of your crewmates, not to mention a multi-billion dollar national asset, all with the eyes of history on your every move? Who would you turn to to really learn the shuttle? Tune in next time when we pick the brain of one of the select few who were tasked with teaching the astronauts how to fly their craft and get it home in one piece.

Ad Astra, catch you on the next pass.